In order to convert motion picture data in the MPEG-2 format to motion picture data in the MPEG-4 format, there has heretofore been adopted a method in which the motion picture data in the MPEG-2 form is decoded into a non-compressed format, and this motion picture data is encoded into the MPEG-4 format, to thereby convert it into the motion picture data in the MPEG-4 format.
Two conventional techniques for converting the motion picture data in the MPEG-2 format to the motion picture data in the MPEG-4 format will be described with reference to FIG. 12 and FIG. 13.
In one conventional technique, as shown in FIG. 12, the conventional motion picture data converter 33 comprises a bit stream input section 34, an MPEG-2 decoder 35, an MPEG-4 encoder 36, and a bit stream output section 37. The motion picture data in the MPEG-2 format is input into the MPEG-2 decoder 35 via the bit stream input section 34. The MPEG-2 decoder 35 decodes the motion picture data in the MPEG-2 format into the non-compressed format, and output it to the MPEG-4 encoder 36. The MPEG-4 encoder 36 encodes the data decoded into the non-compressed format to the motion picture data in the MPEG-4 format, and output this data to the bit stream output section 37. The bit stream output section 37 outputs the motion picture data in the MPEG-4 format.
In the other conventional technique, as shown in FIG. 13, in a motion picture data converter 38, the motion picture data in the MPEG-2 format is input to the bit stream input section 39, and the MPEG-2 format data is decoded into the non-compressed format with the software, using a general-purpose central processing unit 40, and then encoded into the motion picture data in the MPEG-4 format, to thereby output the motion picture data in the MPEG-4 format from the bit stream output section 41.
Whether the conversion of the motion picture data in the MPEG-2 format to the motion picture data in the MPEG-4 is performed using hardware or software, it is necessary to provide the MPEG-2 decoder and the MPEG-4 encoder, or the MPEG-2 decoding program and the MPEG-4 encoding program.
Moreover, in order to confirm the image quality of the motion picture data converted from the MPEG-2 format to the MPEG-4 format, there has heretofore been taken a method of reproducing the motion picture data in the MPEG-2 format before conversion and the motion picture data in the MPEG-4 format after conversion, respectively separately, to compare the image quality of the motion picture.
As described above, with the conventional art, at the time of converting the motion picture data in the MPEG-2 format to the motion picture data in the MPEG-4 format, after the motion picture data in the MPEG-2 format is first decoded into the non-compressed format, all the encoding processing (motion detection, motion compensation, encoding, etc.) of the MPEG-4 format must be executed using the motion picture data in the non-compressed format. Hence, it is necessary to prepare an MPEG-4 encoder that can execute all the processing of motion detection, motion compensation and encoding, thereby causing a problem in that the circuit scale of the apparatus increases. Moreover, when the conventional method is realized as the software for the general-purpose central processing unit, there is a problem in that the processing time increases.
Most of the above-described problems are attributable to the search processing of the motion vectors. The search processing of motion vectors stands for searching the most analogous area with respect to the area to be encoded in the current frame, from the search range in the adjacent frame. The motion vector is expressed as a motion vector from the frame search area in the adjacent frame to the area to be encoded in the current frame.
With the conventional art, at the time of converting the motion picture data in the non-compressed format into the motion picture data in the MPEG-4 format, it is necessary to perform complete survey, using the frame of the non-compressed picture, in the above-described motion vector search processing. Hence, there are such problems that the circuit scale of the apparatus increases, and the processing time increases.
Also, with the conventional art, since the motion picture data in the MPEG-2 format before conversion and the motion picture data in the MPEG-4 format after conversion are reproduced respectively separately, to compare the image quality of the motion picture, the correspondence between the motion picture data before the conversion and the motion picture data after the conversion at the same point in time is incomprehensible, making it difficult to confirm whether the parameters such as the screen size, bit rate, target frame rate, etc. of the motion picture data in the MPEG-4 format are appropriate or not.